/*
 * Copyright 2022 OPPO ESA Stack Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package io.esastack.restlight.core.util;

import esa.commons.Checks;

import java.util.function.Supplier;

public class ThreadSafeLazyValue<T> implements Supplier<T> {

    private static final Object INIT = new Object();

    private final Supplier<T> supplier;
    private volatile Object loaded = INIT;

    public ThreadSafeLazyValue(Supplier<T> supplier) {
        this.supplier = Checks.checkNotNull(supplier, "supplier");
    }

    @SuppressWarnings("unchecked")
    @Override
    public T get() {
        Object load = this.loaded;
        if (load != INIT) {
            return (T) load;
        }
        synchronized (this) {
            load = this.loaded;
            if (load != INIT) {
                return (T) load;
            }

            return (T) (this.loaded = supplier.get());
        }
    }

}
